Flame-retardant regenerated cellulose



States ate ABSTRACT OF THE DISCLOSURE Permanently flame-retardant regenerated cellulose filaments and filamentary articles containing dispersed therein a flame-retardant amount of a substantially waterinsoluble, liquid phosphonitrilate polymer, and a method of preparing the filamentary articles are disclosed herein.

It is desirable, for many textile purposes to provide cellulose fibers and yarns having greatly decreased flammability. The production of rayon which demonstrates permanent and acceptable flame-retardant properties for all textile requirements, using inexpensive and commercially suitable chemical flame-retardants, has not been accomplished to date.

The application of various organic and inorganic flameretardants to the surface of cellulose fibers and fabrics has not produced the desired result for a number of reasons. In many instances, the chemical flame-retardant is effectively removed when the fabric is washed with water or dry cleaned with solvents. Other flame-retardant chemicals which may be applied to the fabric surface and retained after washing are generally too costly. In other cases, the chemicals used may provide some lasting reduction in flammability but destroy fiber and fabric characteristics, such as tenacity, softness, whiteness, and dyeability, which are desirable and necessary for textile applications.

In the manufacture of rayon by the viscose method, it has been proposed to add various flame-retardant chemicals to the viscose prior to spinning. This approach presents many additional problems because of the particular chemistry of the viscose process. Accordingly, the flameretardant must be stable and inert with respect to the highly alkaline viscose and also with respect to the acid regenerated bath into which the viscose is extruded. It must not be extracted during spinning and processing. Furthermore, the added material must not interfere with the spinning process, i.e., cause clogging of the spinnerets. The rayon produced from the flame-retardant containing viscose must not be degraded in any of its properties and must have a substantial and permanently reduced flammability after continued washing and cleaning.

It is an object of this invention to provide a permanent- 1y flame-retardant rayon fiber without appreciable degradation of any fiber properties.

It is another object of this invention to provide a flame-retardant rayon textile that will retain its flameretardant property after continued Washing with alkaline soap and detergents in water or after dry cleaning with organic solvents.

It is still another object of this invention to provide a flame-retardant rayon that is not adversely affected by exposure to ultra-violet light or bleaching solutions.

It is a further object of this invention to provide a process for preparing a permanently flame-retardant rayon fiber.

These and other objects are achieved in accordance with this invention which comprises a regenerated cellulose filament having dispersed therein a substantially water-insoluble, liquid phosphonitrilate polymer having the following general formula:

wherein R and R are the same or different alkyl or alkenyl radicals having from one to six carbon atoms and n in an integer of at least three. For example, R and R include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl, allyl, and crotyl radicals. In a preferred embodiment of this invention R and R are npropyl, isopropyl or allyl radicals since polymers wherein both R and R have fewer carbon atoms tend to be more water-soluble, whereas the presence of more carbon atoms provide products having a lower phosphorous content thereby reducing their effectiveness as flame retardants. This can be overcome, of course, by using polymers wherein R contains fewer carbons and R contains more. For example, R is methyl or ethyl and R is butyl, amyl, isoamyl, or hexyl.

The liquid phosphonitrilate polymer is a cyclic trimer, tetramer or higher cyclic polymer, or a linear polymer and is preferably employed as a mixture of these isomers for economic reasons. It has been found, however, that the pure polymeric isomer is just as effective as the mixture for the purposes of this invention.

The amount of phosphonitrilate flame-retardant dispersed in the regenerated cellulose filament varies from about 1 to about 30% and preferably from 2 to 20%, based on the weight of the filament.

The method of this invention comprises incorporating the above described liquid phosphonitrilate in a viscose solution and spinning the viscose in the shape of one or more filaments into a coagulating and regenerating medium. The formed filaments are aftertreated using techniques well-known in the rayon field to provide continuous filaments, fibers and yarn, as well as staple fibers. These may then be used to prepare any known textile article in which the flame-retardant property is desirable.

The flame-retardant phosphonitrilate of this invention is a liquid of pumpable consistency which is preferably used as a crude reaction product, prepared, for example, in a known manner by the conversion of the corresponding polymeric phosphonitrilic chlorides to the specified esters;

or in a distilled or otherwise refined state. If desired,

suitable solutions of the phosphonitrilate may also be prepared and used for incorporation in viscose.

In a preferred embodiment of the method of this invention, a controlled amount of the flame-retardant phosphonitrilate is injected into the viscose just prior to its extrusion through the spinnerets. The viscose is extruded into an acid bath and processed in a conventional manner.

The following example is set forth to demonstrate the method and product of this invention.

EXAMPLE Excellent flame-retardant rayon yarn with no after-glow was produced from viscose comprising 8.2% cellulose, 6.2% sodium hydroxide and 34.0% carbon disulfide, based on the weight of the cellulose, having a common salt test range of 3.5 to 7.3 and a Ball-Fall range of 52 to seconds at 18 C.

A metered amount, based on the weight of the cellulose in the viscose of a liquid mixture of di-n-propyl phosphonitrilate polymers, as defined for this invention, comprising about 65% trimer, about 15% tetramer, between about 15 and 20% of higher cyclic polymers and less than about 5% of linear polymers, was pumped into the viscose line supplying the spinnerets.

The flame-retardant containing viscose was spun into 3 a bath comprising 9.0% sulfuric acid, 2.0% zinc sulfate and 15.0% sodium sulfate at 55 C. and then further processed by a series of baths including water wash, desulfurization, bleaching, bleach acid, anti-chlorine, and soft finish. The yarn was dried and collected.

Retention of the flame-retardant in the yarn and fabrics produced therefrom is of primary importance and this property of the yarns of this invention was given severe testing. Yarn, and fabric produced therefrom, containing 12.0% of the liquid phosphonitrilate polymer of this in- A yarn flammability test was conducted with yarn pro- 5 vention as disclosed in the foregoing example, based on duced as described above. The test consisted of first preparthe weight of the cellulose, were examined for the reing a yarn bundle by wrapping the yarn around the closed tention of the flame-retardant. fingers of an extended hand to produce a bundle of 6000 The following table sets forth the retention data obdenier and then removing it from the hand. The yarn tained. bundle is twisted five times and then doubled on itself TABLE III to produce an integrated yarn bundle, one and one-half Processing: Percent retention 1 inches long and of 12,000 denier size. The free ends of Complete (as described for Table I) 93.8 the i buildle are it in forceps and the p Soxhlet Extractions: Percent loss 2 held 1n horizontal position, is passed through the t1p of 1,0 cycles water 32 12 3:2 3 222gg fg fiigf gfig 20 y p ether ra e l s adjusted to a two inch height and a blue flame. The 20 clcles penihloroethylene u number of passes to induce flaming of the sample is Commerclal launderlngi 3 Percent 10582 determined. A control yarn bundle (yarn contains no 20 20 cycles flameretardant) mfiames P 1 or 2 Passes f 1 Retention of amount of flame-retardant injected in viscose retardant yarns are classified for mflammabillty as based on phosphorous analysis. follows: 2 Loss from completely processed yarn based on phosphorous prepared from completely processed yarn washed Passes P0913 in automatic washer with 1A cup of sodium oleate per cycle. 2:: gg Yarns and fabrics subjected to the above test propasses Very good to excellent cedures all retaln their excellent flame-retardant properties. 10 or more passes m Excellent. A summary of some of the advantages of this inven- Rayon yarns, prepared as described above, containing tion includes the following points. 20, 15, and 12% of the flame-retardant, based on the The flame-retardant of this invention is a fairly mobile weight of the cellulose, all were rated excellent in the liquid that can be readily pumped and metered into a above test procedure with no evidence of after-glow. Afterviscose solution. Thus, there is no need to make alkaline glow represents combustion without avisible flame. solutions or dispersions which may cause spinning The filaments of this invention, in the form of yarns, problems. were tested for strength characteristics before and after The initial retention of the flame-retardant on spinning complete processing. Complete processing involves treatinto cellulose filaments and fibers is excellent in contrast ing the wet spun yarn in a series of baths as follows: to many hydrolyzable or water-soluble fire-retardants. Water wash, desulfurization, water wash, bleaching, water Surprisingly, there is little or no hydrolysis of this flamewash, bleach acid, water wash, antichlorine, water wash, retardant even when mixed with viscose and allowed to and soft finish. Yarns tested before complete processing stand for up to 18 hours. were merely subjected to one water wash after spinning. There is almost no loss in the alkaline desulfurization The following table sets forth the data obtained from and anti-chlorine baths that are conventionally used in these strength tests with yarns prepared as described processing rayon. Alkali-soluble materials tend to be in the foregoing example. leached from the rayon during processing.

TABLE I Percent phos- Denier/ Yarn phonitriiate Processing filament denier Tc Ec Tw Ew 0.0 Complete 300/60 291 2.5 18.6 12.0-.-

Water-wash 300/60 318 2.07 20.1 1 09 24.2 12.0.-- Complete 300/60 324 1.89 20.2 1 01 24.2 15.0 Water-wash 300/60 331 1.80 18.7 0.96 22.2 15.0 Complete 300/60 402 1. 59 18.8 0.82 22.7 20.0 Water wash 300/00 336 1.76 18.9 0. 91 23 o Tc=Qonditioned tenacity; Ec=Conditioned elongation; Tw=Wet tenacity; Ew=Wet elongation.

Yarn physical characteristics, as compared to similar yarn containing no flame-retardant are excellent even after complete processing.

These yarns were also studied to determine the effect of ultraviolet light thereon. The tests were conducted with a Fadeometer under the same conditions for each yarn sample. The data developed are given in the following table.

TABLE II Percent loss in yarn strength Percent phosphonitrilate hours 100 hours The ultra-violet light strength stability of the flameretardant yarns is even better than the control sample, further demonstrating unexpected results for this invention.

The retention is excellent after many launderings and dry cleanings.

The fire-retardancy of the product of this invention is excellent despite the absence of halogens which often cause ultra-violet light degradation.

Unlike many other nitrogen containing compounds, the liquid phosphonitrilate polymer of this invention has no tendency to pick up chlorine from bleaching solutions which might lead to yellowing and fiber degradation.

The phosphonitrilate polymer is dispersed readily and evenly throughout the fiber because of its liquid nature, and therefore, has little effect on the fiber tensile strength. Such small losses in strength that do occur generally result only from displacement of a certain amount of cellulose.

The appearance and general physical properties of the flame-retardant rayon of this invention differ only slightly from ordinary rayon. Hence, the fibers can be processed in the normal fashion.

Various changes and modifications may be made practicing the invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.

I claim:

1. Regenerated cellulose filaments and filamentary articles, said filaments having dispersed therein a flameretardant amount of a substantially water-insoluble, liquid phosphonitrilate polymer having the following general formula Lei wherein R and R are alkyl or alkenyl radicals having from 1 to 6 carbon atoms and n is an integer of at least 3.

2. The regenerated cellulose filaments of claim 1 containing from about 1 to about 30%, based on the Weight of the cellulose, of the liquid phosphonitrilate polymer.

3. The regenerated cellulose filaments of claim 1 wherein R and R are the same and contain 3 carbon atoms.

4. The regenerated cellulose filaments of claim 3 wherein R and R are n-propyl radicals.

5. The regenerated cellulose filaments of claim 3 Wherein R and R are isOprOpyl radicals.

6. The regenerated cellulose filaments of claim 3 wherein R and R are allyl radicals.

7. A method of preparing a permanently flame-retardant regenerated cellulose filament which comprises mixing viscose and a flame-retardant amount of a substantially water-insoluble, liquid phosphonitrilate polymer having the following general formula:

\ ARJ.

wherein R and R are alkyl or alkenyl radicals having from 1 to 6 carbon atoms and n is an integer of at least 3, shaping the mixture into a filament, and coagulating and regenerating said filament.

8. The method of claim 7 wherein the viscose is passed under pressure to a spinneret and extruded, and the liquid phosphonitrilate polymer is injected at a controlled rate into the viscose prior to extrusion.

9. The method of claim 7 wherein from about 1 to about 30% of the liquid phosphonitrilate is mixed with the viscose, based on the Weight of the cellulose in the viscose.

10. The method of claim 7 wherein R and R are the same and contain 3 carbon atoms.

References Cited UNITED STATES PATENTS 2,192,921 3/1940 Lipkin 260-927 3,266,918 8/1966 Schappel et al. 106l5 XR 3,370,020 2/ 1968 Allcock et a1 260-2 JULIUS FROME, Primary Examiner L. HAYES, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,455,713 July 15, 1969 Leonard E. A. Godfrey It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 27, "7-8" should read 7-9 (SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

